Die casting machine

ABSTRACT

A die casting machine capable of reducing the pressure in a die cavity to a lower level such as a substantially perfect vacuum, having a movable die and a fixed die, a vacuum pump for reducing pressure in a cavity formed between the dies, and an injection apparatus for injecting and filling molten metal into the cavity with reduced pressure, at least one of the dies having an evacuation path connected with the vacuum pump and communicated with the cavity, a valve element for opening and shutting the evacuation path, and an electromagnetic driving means for making the valve element move linearly in the opening and shutting direction by electromagnetic force.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a die casting machine usingvacuum die casting, that is, die casting in a state with pressure in thecavity reduced.

[0003] 2. Description of the Related Art

[0004] A die casting machine is provided with a pair of dies, a fixeddie plate and a movable die plate for holding these dies, a clampingapparatus for clamping the dies, an injection apparatus for injectingmolten metal into a cavity formed between the dies, a molten metalsupplying apparatus for supplying the molten metal to the injectionapparatus, and so on. In such a die casting machine, a die casting isobtained by clamping the dies, supplying molten metal into a sleeve ofthe injection apparatus, injecting the molten metal into the cavity, andfilling the cavity with the molten metal.

[0005] One of the causes of uneven quality of die castings is theinclusion of gas in the die castings. That is, molten metal injectedinto the cavity and filled in the cavity at a high speed and under ahigh pressure forms a turbulent flow in the sleeve and the cavity. Dueto this, gas such as air or vaporized parting agent is mixed into themolten metal.

[0006] In order to overcome the above problem, there is known the vacuumcasting method for decreasing the inclusion of gas and reducingunevenness of die castings caused by the inclusion.

[0007] In a die casting machine using the vacuum casting method, asdisclosed for example in U.S. Pat. No. 2,785,448, the inclusion of gasinto the molten metal is suppressed by injecting the molten metal intothe cavity and filling the cavity with the molten metal in a state withthe pressure reduced by a vacuum pump.

[0008] In the above die casting machine using vacuum casting, in orderto cast a product with a high strength and high quality, it is requiredto be able to create a higher vacuum in the cavity and maintain thevacuum state.

[0009] If the cavity is not made a high vacuum, it is difficult toobtain enough of an effect by the vacuum die casting, because gasbecomes included in the casting and distortion or a deformation of theproduct easily occurs when annealing or otherwise heat treating theproduct after casting.

[0010] In order to cast a product with a higher strength and a higherquality, specifically, it is desired to reduce the pressure in thecavity to several tens of Torr.

[0011] Further, from the viewpoint of improving the productivity of adie casting machine, it is required to shorten the time required forevacuation by the vacuum pump as far as possible.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a die castingmachine using vacuum casting capable of achieving a higher vacuum in thecavity.

[0013] According to a first aspect of the present invention, there isprovided a die casting machine comprising a movable die and a fixed die,a vacuum pump for reducing pressure in a cavity formed between the dies,and an injection apparatus for injecting and filing molten metal intothe cavity at a reduced pressure, at least one of the dies including anevacuation path connected with the vacuum pump and communicated with thecavity, a valve element for opening and shutting the evacuation path,and an electromagnetic driving means for making the valve element movelinearly in the opening and shutting direction by electromagnetic force.

[0014] In the first aspect according the present invention, since anelectromagnetic driving means is used for driving the valve element foropening and shutting the evacuation path formed in the die, it becomespossible to rapidly move the valve element.

[0015] Further, in the first aspect of the present invention, the valveelement may be arranged between the parting faces and form a valve seatportion integrally with a die. Due to this, it becomes possible toreliably open and shut the evacuation path.

[0016] According to a second aspect of the present invention, there isprovided a die casting machine comprising a movable die and a fixed die,a vacuum pump for reducing pressure in a cavity formed between the dies,an injection apparatus for injecting and filing molten metal into thecavity with a reduced pressure, an ejecting pin, for ejecting a productformed in the cavity, inserted into an insertion hole formed in a dieand communicated with the cavity, a sealing member for sealing betweenthe ejecting pin and the insertion hole to prevent air from flowing intothe reduced pressure cavity, and a temperature rise prevention means forpreventing a rise in the temperature of the ejecting pin due to contactwith the formed product.

[0017] In the second aspect according the present invention, thetemperature rise prevention means is provided to prevent a sealingmember such as an O-ring from being damaged by heat.

[0018] Due to this, it becomes possible to keep the cavity sealedreliably by the sealing member and prevent air from flowing in and tocreate a high vacuum in the cavity.

[0019] According to a third aspect of the present invention, there isprovided a die casting machine comprising a movable die and a fixed die,a vacuum pump for reducing pressure in a cavity formed between the dies,and an injection apparatus for injecting and filing molten metal intothe cavity with a reduced pressure, at least one of the dies includingan evacuation path connected with the vacuum pump and communicated withthe cavity, a plurality of valve elements for opening and shutting theevacuation path, a plurality of electromagnetic driving means for movingthe valve elements linearly in the opening and shutting direction byelectromagnetic force, and a control means for independently controllingthe drive operations of the electromagnetic means.

[0020] In the third aspect according the present invention, byindependently controlling a plurality of electromagnetic means, itbecomes possible to shorten the time required to create a high vacuum inthe cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These and other objects and features of the present inventionwill become clearer from the following description of the preferredembodiments given with reference to the accompanying drawings, in which:

[0022]FIG. 1 is a view of an example of the configuration of a diecasting machine to which the present invention is applied;

[0023]FIG. 2 is a view of a die-opening state of the die casting machineshown in FIG. 1;

[0024]FIG. 3 is a view of the configuration around the dies according tothe first embodiment of the present invention;

[0025]FIG. 4 is a view of the configuration of the parting face of thefixed die;

[0026]FIG. 5 is a view of the configuration of the parting face of themovable die;

[0027]FIG. 6 is a sectional view of the configuration around the valvemechanism 21;

[0028]FIG. 7 is a sectional view of the concrete configuration of theseal cooling mechanism 61;

[0029]FIG. 8 is a view for explaining the operational state of the valvemechanism 21;

[0030]FIG. 9 is a view for explaining the relationship between thereduced pressure and the injection speed in the cavity;

[0031]FIG. 10 is a sectional view of the configuration around the diesaccording to the second embodiment of the present invention; and

[0032]FIG. 11 is a view for explaining the relationship between thereduced pressure and the injection speed in the cavity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Below, preferred embodiments will be described with reference tothe accompanying drawings.

[0034] First Embodiment

[0035]FIG. 1 is a view of an example of the configuration of the diecasting machine to which the present invention is applied.

[0036] In FIG. 1, the die casting machine I is provided with a base 100,a fixed die plate 91 arranged on the base 100, a fixed die 2 attached tothe fixed die plate 91, an injection apparatus 95 arranged on theopposite side of the fixed die plate 91 from the fixed die 2, a movabledie plate 3 arranged on the base 100 facing the fixed die 2, a movabledie 3 attached to the movable die plate 3 facing the fixed die 2, a linkhousing 71 connected to the fixed die plate 91 by tie bars 80 throughthe movable die plate 92, and a toggle die clamping mechanism 109consisting of a plurality of links which connects the link housing 71and the movable die plate 92.

[0037] The fixed die plate 91 is fixed on the base 100, while themovable die plate 92 is arranged movably on the base 100.

[0038] The link housing 71 and the fixed die plate 91 are connected by aplurality of tie bars 80 which pass through the movable die plate 92.Normally, there are four tie bars.

[0039] The toggle die clamping mechanism which connects the link housing71 and the movable die plate 51 is provided with two pairs of linksystems 110, only one of which is shown in detail in FIG. 1. FIG. 1shows the configuration of one of the pairs in detail. Each of linksystems is provided with an angled first link 110-1 and a straightsecond link 110-2. The first link 110-1 has an end pivoted to the linkhousing 71 and another end pivoted to a cross head 105. The second link110-2 has an end pivoted to the first link 110-1 at a location betweenthe pivot points to the link housing 71 and the cross head 105 andanother end pivoted to the movable die plate.

[0040] This cross head 72 pivoted to the first link 110-1 of the toggledie clamping mechanism 109 is moved in a direction as shown by arrows A1and A2 along the screw shaft 106, whereby the toggle die clampingmechanism 109 operates and causes the link housing 71 to be moved to ormoved away from the movable die plate 92.

[0041] The screw shaft 73 is driven by a not illustrated servo motorarranged at the link housing 71. By the rotation of the screw shaft 73,the cross head 72 engaged with the screw shaft 73 is moved in,thedirection as shown by the arrows A1 and A2.

[0042] As shown in FIG. 1, when the cross head 72 is moved in thedirection as shown by the arrow A2 by driving the not illustrated servomotor, the toggle die clamping mechanism 109 is operated and the movabledie plate 92 is moved in the direction away from the link housing 71 toclose the fixed die and movable die. Further movement of the cross head72 in the direction of the arrow A2 causes the tie bars 80 to betensioned and the fixed die 2 and the movable die 3 to be clamped.

[0043] The injection apparatus 95 injects and fills molten metal into anot illustrated cavity formed between the clamped fixed die and movabledie. By solidification of the molten metal injected into and filling thecavity, a die casting can be obtained.

[0044] On the other hand, when taking out the die casting from the diesafter casting, as shown in FIG. 2, the cross head 72 is moved in thedirection of the arrow A1. This causes the movable die plate 92 to bemoved in a direction toward the link housing 71, i.e., the die openingdirection, so that the movable die plate 3 is opened from the fixed dieplate 2. When opening the movable die 3 from the fixed die 2, the diecasting is moved together with the movable die 3. This die casting stuckin the movable die 3 is pushed out and ejected from the movable die 3 bythe ejecting mechanism explained below.

[0045]FIG. 3 is a sectional view of the configuration around the diesaccording to the embodiment of the present invention. Further, FIG. 4 isa view of the configuration of a contact face (parting face) of thefixed die 2, while FIG. 5 is a view of the configuration of a contactface (parting face) of the movable die 3. Note that the fixed die 2 andthe movable die 3 shown in FIG. 3 are in a clamped state.

[0046] As shown in FIG. 3, the injection apparatus 95 is arranged at theback side of the fixed die 2.

[0047] The injection apparatus 95 is provided with a cylindrical sleeve96 arranged at the back side of the fixed die 2, a plunger tip 97 fitinto the inner circumference of this sleeve 96, a plunger rod 98connected with the plunger tip 97 at its end, and an injection cylinderapparatus 99 connected with the other end of the plunger rod 98.

[0048] The sleeve 96 is provided with a supply port 96 a. Molten metalML is supplied into the sleeve 96 through this supply port 96 a by aladle 100.

[0049] The injection cylinder apparatus 99 incorporates a piston. Apiston rod 99 a connected with this piston and the plunger rod 98 areconnected by a coupling 99 b. This injection cylinder apparatus 99 isdriven by hydraulic pressure to extend and retract the piston rod 99 a.

[0050] The plunger tip 97 is connected to the plunger rod 98 and ismoved in the sleeve 96 by a drive operation of the injection cylinderapparatus 99. The movement of the plunger tip 97 in the sleeve 96supplied with the molten metal ML toward the side of the fixed die 2causes the molten metal to be filled in the cavity throughout a runnerportion Rn formed by the fixed die 2 and the movable die 3.

[0051] Note that a sensor 98 a detects the number of magnetic poles Nand S, formed on the periphery of the plunger rod 98 at a predeterminedpitch in an axial direction, which are passed as a pulse signal. Theinjection speed of the plunger tip 97 is detected based on the number ofpulses of this pulse signal.

[0052] The output of the sensor 98 a is supplied to a machine controller52. A current position counter 52 a in the machine controller 52 detectsthe position of the plunger tip 97 based on a pulse signal from thesensor 98 a.

[0053] Further, reference numeral 52 b shows a register for setting aposition where the plunger tip 97 passes a molten metal supply port ofthe sleeve 96, while reference numeral 52 c shows a register for settinga position to change the injection speed of the plunger tip 97 to ahigher injection speed. When the value of the counter 52 a reaches thevalue of either of the registers 52 b and 52 c, the machine controller52 issues a valve controller 51 a command to open or shut the valve of acorresponding hydraulic system for driving the plunger tip 97.

[0054] The runner portion Rn is formed from channels Rna formed on theparting face 3 a of the movable die 3 shown in FIG. 5 and the partingface 2 a of the fixed die 2.

[0055] The cavity C is formed from a curved surface Ca formed in theparting face 2 a of the fixed die 2 shown in FIG. 4 and a curved surfaceCb formed in the parting face 3 a of the movable die 3 shown in FIG. 5corresponding to the shape of die casting.

[0056] As shown in FIG. 3, an evacuation path Ep is formed above thecavity C. This evacuation path is formed from a channel Epa communicatedwith the curved surface Cb formed in the parting face 3 a of the movabledie 3 shown in FIG. 5 and a channel Epb formed in the face 2 a of thefixed die 2 shown in FIG. 4. Note that a recess Sa adjoining the channelEpb is a contact portion of a valve described below.

[0057] As shown in FIG. 3, a valve mechanism 21 is arranged so as to becommunicated with the evacuation path Ep formed between the parting face2 a of the fixed die and the parting face 3 a of the movable die 3.

[0058] An explanation will be made of the configuration around thisvalve mechanism 21 with reference to FIG. 6.

[0059] As shown in FIG. 6, the valve mechanism 21 is provided with anelectromagnetic actuator 22, a valve shaft connected to theelectromagnetic actuator 22, and a disc-shaped valve element 24 formedintegrally at the front end of the valve shaft 23.

[0060] The valve shaft 23 and the valve element 24 are made of a metalmaterial such as stainless steel.

[0061] The electromagnetic actuator 22 is fixed on an opening end 29 bof a cup-shaped guide member 29 via a flange member 32. The cup-shapedguide member is inserted and tightly fit into an insertion hole 3 hformed in the movable die 3.

[0062] An O-ring made of a plastic is interposed between the guidemember 29 and the insertion hole 3 h formed in the movable die 3 to sealthem.

[0063] A guide hole 29 a is formed at the bottom portion of the guidemember 29. The valve shaft 23 is movably inserted and tightly fit intothis guide hole 29 a. From the viewpoint of the stability at the time ofmovement, the portion which fits in the guide hole 29 a is made largerin diameter than the valve element 24 side. Further, the valve shaft isprecisely fit with the guide hole 29 a, so the space between the guidehole 29 a and the valve shaft 23 is sealed.

[0064] The valve shaft 23 has a hollow portion 23 a inside. This is tomake the speed of movement of the valve shaft 23 higher by lighteningthe weight and reducing the inertia of the valve shaft 23.

[0065] In the movable die 3, an evacuation path 26 communicated with theabove evacuation path Ep and for insertion of the valve shaft 23 isformed in a direction vertical to the parting face 3 a of the movabledie 3. Note that the portion of the movable die 3 where the evacuationpath 26 is formed is formed by a different metal member 3 d for assemblyof the valve mechanism 21 in the movable die 3.

[0066] A valve seat portion 39 is formed at the front end of theevacuation path at the parting face 3 a side. This valve seat portion 39faces the valve element 24 and shuts the evacuation path 26 by contactof the valve element 24 with a valve seat 39 a formed on it. Note thatthe valve seat 39 a is formed along the parting face 3 a of the movabledie 3.

[0067] This valve seat portion 39 is made of a material which is softerthan that of the valve element 24. Specifically, the material is a metalsuch as a copper alloy.

[0068] An evacuation path 25 is formed in the movable die 3 along adirection crossing the evacuation path 26 at right angles. Theevacuation path 25 is communicated with the evacuation path 26. Anattachment hole 3 g is formed above this evacuation path 25. Anevacuation pipe 55 is inserted in this attachment hole 3 g.

[0069] The evacuation pipe 55 is formed with a thread on the outercircumference at the front end. This thread engages with a thread formedat the inner circumference of the attachment hole 3 g.

[0070] Further, a ring member 59 is fixed around the top end side of theattachment hole 3 g via O-rings 59 a and 59 b made of plastic to sealthe space between the evacuation pipe 55 and the attachment hole 3 g.

[0071] The electromagnetic actuator 22 has a shaft member 22 a connectedwith the valve shaft 23, a not illustrated permanent magnet fixed tothis shaft member 22 a, and a not illustrated electromagnet arrangedaround this permanent magnet inside of its case.

[0072] By supplying the electromagnet with electric power from theoutside, an attraction force occurs between the permanent magnet and theelectromagnet so that the shaft member 22 a is moved linearly.

[0073] The electromagnetic actuator 22 drives the valve element 24 in adirection to open or shut the evacuation path 26 as shown by arrows C1and C2 in FIG. 6 by suitably changing the direction of the currentsupplied to the electromagnet.

[0074] As shown in FIG. 3, this electromagnetic actuator 22 iselectrically connected to the valve controller 51 and is supplied withelectric power from the valve controller 51.

[0075] The valve controller 51 controls the drive operation of theelectromagnetic actuator 22 to open or shut the valve element 24. Thisvalve controller 51 is electrically connected to the machine controller52 generally controlling the die casting machine 1 and controls theelectromagnetic actuator 22 in response to a signal input from themachine controller 52.

[0076] As shown in FIG. 3, the above evacuation pipe 55 is connected toa vacuum pump 50. This vacuum pump 50 evacuates air in the cavitythrough the evacuation pipe 55, the evacuation path 25, the evacuationpath 26, and the evacuation path Ep. As the vacuum pump, one which canevacuate the cavity to create a high vacuum of several to several tensof Torr is used.

[0077] The parting face 3 a of the movable die 3 is formed with achannel 3 b in which a sealing member 35 is laid. Part of the sealingmember 35 sticks out from the parting face 3 a. When the parting face 3a of the movable die 3 contacts the parting face 2 a of the fixed die 2,the sticking out portion of the sealing member 35 contacts the partingface and seals between the parting face 2 a and the parting face 3 a.

[0078] Preferably, the sealing member 35 is made of a relatively highheat resistant material such as silicone rubber. Note that aconfiguration where the sealing member 35 is laid in the parting face 2a can also be employed.

[0079] As shown in FIG. 5, the sealing member 35 is arrangedcontinuously at the periphery of the parting face 3 a of the movable die3 without break.

[0080] Further, the evacuation path Ep, the cavity C, and the runnerportion Rn are arranged inside from the sealing member 35 and aresufficiently away from the sealing member 35.

[0081] Next, an explanation will be made of a specific configuration ofthe ejecting mechanism 41.

[0082] As shown in FIG. 3, the ejecting mechanism 41 is arranged at theback side of the movable die 3.

[0083] The ejecting mechanism 41 is provided with a plurality ofejecting pins 42, holding plates 43, 44 for holding ends of the ejectingpins 42, a movable plate 45 to which the holding plates 43, 44 arefixed, a guide shaft 46 for movably guiding the movable plate 45 to themovable die 3, and a seal cooling mechanism 61.

[0084] The ejecting pins 42 are formed by metal members of stainlesssteel etc. and are inserted and tightly fit into insertion holes 46formed in the movable die 3. Note that, as below described, theinsertion holes tightly fit with the ejecting pins 42 at only the partsnear the parting face 3 a of the movable die 3 and are enlarged indiameter at the other parts to allow the pins to easily slide.

[0085] As shown in FIG. 5, the insertion holes 3k open at the partingface 3 a of the movable die 3. The insertion holes 3 k are arrangedfacing the runner portion Rn, periphery of the cavity, or evacuationpath Ep. By extension of the front ends of the ejecting pins 42 fromthese insertion holes 3 k, the die casting stuck in the movable die 3can be ejected.

[0086] The holding plates 43 and 44 grip the enlarged diameter rear endsof the ejecting pins 42. These holding plates 43 and 44 are fixed on themovable plate 45.

[0087] As shown in FIG. 3, the movable plate 45 is movably guided in thedirection of the arrows E1 and E2. This movable plate 45 is moved by anot illustrated driving means in the direction of the arrows E1 and E2within a predetermined range. By the movement of the movable plate 45 inthe direction of the arrows E1 and E2, the front ends of the ejectingpins 42 protrude from the parting face 3 a of the movable die 3.

[0088] The ejecting pins 42 tightly fit with the insertion holes 3 k, sothere is no possibility that the molten metal will invade a spacebetween the ejecting pins 42 and the insertion holes 3 k, but there ispossibility that air will enter between the ejecting pins 42 and theinsertion holes 3k. If air can enter between the ejecting pins 42 andthe insertion holes 3 k, it will be impossible to make the cavity a highvacuum when reducing the pressure in the cavity.

[0089] Further, because the ejecting pins 42 directly contact the hightemperature die casting, there is possibility that the temperature ofthe ejecting pins 42 will also become high. Therefore, when sealing thespaces between the ejecting pins 42 and the insertion holes 3 k withsealing members (O-rings) made of plastic, there is a possibility thatthe O-rings will not be able to endure the high temperature andtherefore continuous use of the O-rings will become impossible.

[0090] In the present embodiment, in order to solve the above problem, aseal cooling mechanism is arranged at the back side of the movable die3.

[0091]FIG. 7 is a view of a concrete configuration of the seal coolingmechanism 61.

[0092] As shown in FIG. 7, the seal cooling mechanism 61 has aplate-shaped first member 63 having a recess 63 h, a plate-shaped secondmember 64 fixed to the first member 63 at the recess 63 h side, and aseal holding member 65 (only one shown) fixed to the first member 63 andthe second member 64. Note that here, while only one seal holding member65 is shown and the explanation is given of only one such member, inpractice there are a plurality of members corresponding to the number ofejecting pins.

[0093] The first member 63 is fixed to the second member to form acoolant storage space Sa comprised of the recess 63 h of the firstmember 63 and the opposing face of the second member 64. Between thefirst member 63 and the second member 64 is interposed an O-ring 75 madeof plastic to seal the first member 63 and the second member 64.

[0094] The second member 64 is fixed to the back face of the movable die3. A plastic O-ring 74 is interposed at the periphery between the secondmember 64 and the back face of the movable die 3 to seal the secondmember 64 and the back face of the movable die 3.

[0095] A recess 64 a is formed in the surface of the second member 64facing the movable die 3 positioned at the inside of the O-ring 74. Aspace S is formed between the movable die 3 and the second member 64.

[0096] A supply port 63 b for supplying the coolant storage space Sawith a coolant W and an outlet 63 c for discharging the coolant W areformed in the peripheral wall of the first member 63.

[0097] The seal holding member 65 is formed of a cylindrical member andhas an enlarged diameter at the end at the back side of the movable die3. Further, the seal holding member 65 is inserted and tightly fit atits outer circumference into an insertion hole 63 a formed in the firstmember 63 and an insertion hole 64 b formed in the second member 64 soas to be fixed to the first member 63 and the second member 64. O-rings72 and 73 made. of plastic are held at the inner circumferences of theinsertion hole of the first member 63 and the insertion hole 64 b of thesecond member 64.

[0098] These O-rings 72 and 73 seal the outer circumference of the sealholding member 65 and the insertion hole 63 a and the outercircumference of the seal holding member 65 and the insertion hole 64 b.

[0099] The seal holding member 65 is provided with a through hole 65 ain the center into which an ejecting pin 42 is inserted and tightly fit.An O-ring made of plastic is held at the inner circumference of thisthrough hole 65 a at the second member 64 side, while an O-ring 71 madeof plastic is held at the inner circumference at the first member 63side.

[0100] The O-rings 70, 71 seal the ejecting pin 42 and the through hole65 a.

[0101] Further, the seal holding member 65 is provided with a hollowportion 65 c and a through hole 65 b formed in the direction crossingthe ejecting pin 42 at right angles.

[0102] In the above seal cooling mechanism 61, the supply port 63 b ofthe first member 63 is connected with a coolant supplying pipe 30. Acoolant W is supplied to the seal cooling mechanism 61 through thecoolant supplying pipe 30. As the coolant W, water for example can beused.

[0103] The coolant supplied from the coolant supplying pipe 30 isintroduced into the coolant storage space Sa. Part of the coolant W issupplied to the hollow portion 65 b through the through hole 65 b of theseal holding member 65.

[0104] The coolant supplied to the hollow portion 65 b cools the part ofthe ejecting pin 42 exposed at the hollow portion 65 c.

[0105] Accordingly, the ejecting pin 42 in the vicinity of the hollowportion 65 c is partially cooled. By continuously supplying the coolantW from the coolant supplying pipe 30, fresh coolant is circulated aroundthe hollow portion 65 c and discharged to the outlet 63 c through thethrough hole 65 b.

[0106] On the other hand, out of the O-ring 70 and O-ring 71 whichtightly fit with the outer circumference of the ejecting pin 42, theO-ring 70 functions to prevent air from entering from outside to betweenthe insertion hole 3 k formed in the movable die 3 and the ejecting pin42 and to prevent the coolant W from entering into the insertion hole 3k. The O-ring 71 functions to prevent the coolant from leaking outsidefrom the coolant storage space Sa.

[0107] If these O-rings 70 and 71 were formed of a heat resistantmaterial such as silicone rubber or a fluororubber, the O-rings 70 and71 would not be able to endure continuous use under an environment wherethe ejecting pin 42 reaches a high temperature such as over 200° C.

[0108] In this embodiment, therefore, even if the temperature of theejecting pin 42 rises by contact of the ejecting pin 42 with a hightemperature die casting, because a hollow portion 65 c is arrangedaround the O-rings 70, 71, the temperature of the part of the ejectingpin 42 contacting the O-rings 70 and 71 is kept below 100□ C. As aresult, the O-rings 70 and 71 are not damaged by heat.

[0109] Next, an explanation will be made of an example of the operationof the above die casting machine 1.

[0110] First, from the state of the die casting machine 1 shown in FIG.2, that is, from the state where the movable die 3 is opened from thefixed die 2, the machine controller 52 operates the toggle die clampingmechanism 110 to clamp the fixed die 2 and the movable die 3.

[0111] By clamping the fixed die 2 and the movable die 3, the sealingmember 35 seals the parting face 2 a of the fixed die 2 and the partingface 3 a of the movable die 3.

[0112] At the time of startup of the die casting machine 1, the aboveseal cooling mechanism 61 is already supplied with the coolant W.

[0113] Further, at the time of startup of the die casting machine 1, thevacuum pump is also started, but the valve element 24 of the valvemechanism 21 shuts the evacuation path 26. Therefore, the cavity is notevacuated.

[0114] On the other hand, the sleeve 96 of the injection apparatus 95 issupplied with a predetermined amount of molten metal such as aluminumalloy by the ladle 100.

[0115] When the ladle 100 finishes supplying the molten metal, theplunger tip 97 is driven under the control of the machine controller 52.When the front end of the plunger tip 97 passes the supply port 96 a ofthe sleeve 96, the sleeve is sealed by the plunger tip 97 to cut offentry of air to the cavity C from the sleeve 96 side.

[0116] Note that the plunger tip 97 is driven normally at a low speedwhen starting to move the plunger tip 97.

[0117] The machine controller 52 judges when the plunger tip 97 haspassed the supply port 96 a of the sleeve 96 and outputs a command toopen the valve element 24 of the valve mechanism 21 to the valvecontroller 51.

[0118] Receiving the command from the machine controller 52, the valvecontroller 51 supply electric power for driving the electromagneticactuator 22 of the valve mechanism 21 to the electromagnetic actuator.

[0119] When the electromagnetic actuator 21 is driven, as shown in FIG.8, the valve element 24 is moved in the direction of the arrow C2,contacts a contact face Sa formed at the parting face 2 a of the fixeddie 2, and stops.

[0120] At this time, because the valve element 24 is driven by theelectromagnetic actuator 22, it takes a substantially constant time ofmore than several ms or less than 20 ms to open the valve element 24.For example, in case of using a hydraulic cylinder to drive the valveelement 24, it takes 200 some odd milliseconds until the valve element24 is completely opened. Further, this time is uneven.

[0121] By this movement of the valve element 24, a space is formedbetween the valve element 24 and the valve seat 39 a. Air (gas) in thecavity is evacuated from this space between the valve element 24 and thevalve seat 39 a through the evacuation path Ep communicated with thecavity C, the evacuation path 26, the evacuation path 25, and theevacuation pipe 55.

[0122] The sealing member 35 seals reliably the parting face 2 a of thefixed die 2 and the parting face 3 a of the movable die 3. Further,because the O-rings 70 arranged at the seal cooling mechanism 61reliably seal the ejecting pins 42 and the movable die 3, the pressurein the cavity is rapidly reduced.

[0123] Here, an explanation will be made of the relation between thepressure reduction in the cavity and the injection speed with referenceto the graph shown in FIG. 9.

[0124] The curve (1) shown in FIG. 9 shows the pressure reduction in thecavity. The curve (2) shows the injection speed of the plunger tip 97.Note that the curve (3) shows a comparative example of pressurereduction in a cavity when operating a valve using a conventionalsolenoid valve and hydraulic or air cylinder apparatus. The curve (4)shows the pressure reduction in the cavity when closing an evacuationpath by driving a valve with inertia of molten metal injected and filledin the cavity. The curves (3) and (4) show the pressure reduction in adie casting machine not provided with the seal cooling mechanism 61 andthe continuous sealing member between the parting face 2 a of the fixeddie 2 and the parting face 3 a.

[0125] As shown by the curve (1), if the time of start of pressurereduction is pt1, because of the good response of the valve element 24,the pressure in the cavity is rapidly reduced from the pressurereduction start time pt1. Further, because there is almost no leakage ofair between the ejecting pins and the die or between the parting face 2a of the fixed die 2 and the parting face 3 a of the movable die 3, itis understood that the pressure in the cavity is efficiently reduced ina short time.

[0126] On the other hand, in the curve (3) or the curve (4), because ofusing a cylinder apparatus to drive the valve, the time lag from thepressure reduction start time pt1 until the pressure reduction actuallystarts is relatively long and there is leakage of air from between theejecting pins and the die or between the parting face 2 a of the fixeddie 2 and the parting face 3 a of the movable die 3. Therefore, thepressure in the cavity is not efficiently reduced.

[0127] Along with movement of the plunger tip 97, the runner portion Rncommunicating with the cavity C and the sleeve 96 is also filled withthe molten metal ML. In this state, the cavity becomes a high vacuum ofabout 20 to 40 Torr.

[0128] The molten metal is injected into and fills the cavity bychanging the injection speed of the plunger tip 97 to a high speed. Thatis, the injection speed is changed to a high speed at the high speedinjection start time pt2.

[0129] However, it is necessary to shut the evacuation path by the valveelement 24 to prevent the molten metal ML from intruding into the valvemechanism 21 before changing to high speed injection.

[0130] Preferably, the timing for shutting the evacuation path 26 by thevalve element 24 is immediately before the high speed injection starttime pt2. That is, this is because there is possibility that aftershutting the evacuation path 26 by the valve element 24, the cavity Cwill not be evacuated and the pressure in the cavity will rise due toleakage of air.

[0131] In the present embodiment, however, because of using theelectromagnetic actuator 22 for driving the valve element 24 and makingthe valve shaft 23 light in weight, it is possible to shut theevacuation path 26 in a short time of as much as several ms to less than20 ms. Further, because there is almost no unevenness of the response ofthe electromagnetic actuator 22, it becomes possible to inject themolten metal into the cavity immediately before the high speed injectionstart time pt2.

[0132] Note that the timing for shutting the evacuation path 26 by thevalve element 24 is determined by the machine controller 52 based on thedetected position of the plunger tip 97 and the detected pressure in thecavity. The machine controller 52 outputs a command to the valvecontroller 51 in response to these position signal and pressure signal.

[0133] When driving the electromagnetic actuator 22 and shutting theevacuation path 26 by the valve element 24, there is possibility thatthe valve element 24 will rebound and jump up because it strikes thevalve seat 39 a of the valve seat portion 39 at a high speed.

[0134] However, in the present embodiment, it is possible to suppressthe jump of the valve element 24 when the valve element 24 strikes thevalve seat portion 39, because of use of a material suppressing reboundto form the valve seat portion 39, that is, a softer material than thevalve element 24. As a result, it is possible to prevent the moltenmetal from intruding into the valve mechanism 21 by mistake.

[0135] When changing to the high speed injection at the high speedinjection start time pt2, the molten metal ML is filled in the cavity Cand then solidified. Due to this, a desirable die casting can beobtained.

[0136] In order to eject the formed die casting from the fixed die 2 andthe movable die 3 clamped together, the toggle die clamping mechanism isoperated to open the movable die 3 from the fixed die.

[0137] When the movable die 3 is opened from the fixed die 2 (at thistime, the plunger tip is pushing a biscuit following the runner portionRn), the formed die casting is separated from the fixed die 2.

[0138] By operating the ejecting mechanism 41 in this state to extendthe ejecting pins 42 from the parting face 3 a of the movable die 3, itbecomes possible to eject the die casting from the movable die 3.

[0139] At this time, because the ejecting pins 42 directly touch thehigh temperature die casting, the temperature of the ejecting pins 42also rises.

[0140] The seal cooling mechanism 61 partially cools the ejecting pins42, so the O-rings 70 and 71 are not exposed to a high temperature andthe function of the O-rings 70 and 71 is not damaged by heat.

[0141] Further, the seal cooling mechanism 61 is continuously suppliedwith the coolant W, so the temperature of the seal cooling mechanism 61falls sufficiently compared with the temperature of the movable die 3.

[0142] Due to this, if the seal cooling mechanism 61 were to directlycontact the movable die 3, the temperature distribution of the movabledie 3 might be influenced and the quality of the die casting might fall.In the present embodiment, however, because a space is formed betweenthe seal cooling mechanism 61 and the movable die 3, the seal coolingmechanism 61 does not directly contact to the movable die 3 and itbecomes possible to keep the seal cooling mechanism 61 from affectingthe movable die 3.

[0143] As described above, according to the present embodiment, by usingthe electromagnetic actuator 22 to drive the valve element for openingand shutting the evacuation path communicating the cavity C and thevacuum pump, it becomes possible to rapidly open and shut the evacuationpath. Because the electromagnetic actuator 22 is driven by electricpower, it is not necessary to supply an operating fluid and it becomespossible to make the valve mechanism 21 compact. Due to this, thefreedom of arrangement of the valve mechanism 21 with respect to thedies increases so that it becomes easy to optimize the arrangement ofthe valve element and the evacuation path communicating between thecavity C and the vacuum pump.

[0144] Because the arrangement of the evacuation path communicating thecavity C with the vacuum pump 50 can be optimized, it becomes possibleto interpose the sealing member 35 between the peripheries of theparting face 2 a of the fixed die 2 and the parting face 3 a of themovable die 3 without break, secure fully the distance between theevacuation path communicating the cavity C with the vacuum pump 50 andthe sealing member 35, and prevent the sealing members from beingdamaged by heat.

[0145] Further, according to the present embodiment, by partiallyforce-cooling the ejecting pins liable to rise to a high temperature,general use sealing members such as O-rings can be easily used to sealbetween the ejecting pins 42 and the die.

[0146] Second Embodiment

[0147]FIG. 10 is a sectional view of the configuration around the diesof a second embodiment of a die casting machine according to the presentinvention. In FIG. 10, the same reference numerals are used for the sameparts of the above described embodiment.

[0148] As shown in FIG. 10, a plurality of valve mechanism 201 and 202are arranged at the movable die of the die casting machine.

[0149] The configuration of the valve mechanisms 201 and 202 is the sameas that of the above valve mechanism 21.

[0150] The valve mechanisms 201 and 202 are arranged in the middle ofthe evacuation path Ep formed between the parting face 3 a of themovable die 3 and the parting face 2 a of the fixed die 2. Theevacuation path is communicated with the cavity C.

[0151] The evacuation path Ep is communicated with a vacuum pump 501 viaevacuation paths 301 and 302 formed corresponding to the valve mechanism201 and is communicated with a vacuum pump 502 via evacuation paths 303and 304 formed corresponding with the valve mechanism 202 in the movabledie 3.

[0152] The vacuum pump 501 is provided with an evacuation ability equalto that of the vacuum pump 502.

[0153] The electromagnetic actuators 22 of the valve mechanisms 201 and202 are connected commonly with the valve controller 51.

[0154] This valve controller 51 can drive the valve mechanisms 201 and202 independently.

[0155] As described above in the first embodiment, by using theelectromagnetic actuator 22 to drive a valve element 24, it becomespossible to make the valve mechanism more compact and increase thefreedom of the arrangement with respect to the die.

[0156] Due to this, it is possible to easily arrange the valvemechanisms with respect to the die.

[0157] As mentioned above, by arranging the plurality of valvemechanisms 201 and 202 at the die, it becomes possible to enlarge thetotal sectional area of the evacuation path for evacuation compared withthe case of arranging a single valve mechanism with respect to the die.Therefore, it becomes possible to efficiently evacuate the cavity C.That is, when arranging a single valve mechanism at the die, even if theevacuation ability of the vacuum pump is enhanced, it is not possible torapidly reduce the pressure in a short time because the sectional areaof the evacuation path is small. By arranging a plurality of valvemechanisms 201 and 202 at the die and enabling the valve mechanisms 201and 202 to be independently driven, it becomes possible to optimize theopening and shutting timings of the valves in accordance with thearrangement of the valve mechanisms.

[0158] Next, an example will be made of the pressure reduction operationin the cavity C in the case of using the plurality of valve mechanismwith reference to FIG. 11.

[0159] In FIG. 11, the curve (1) shows the pressure reduction in thecavity, while the curve (2) shows the injection speed of the plunger tip97.

[0160] First, the movement of the plunger tip 97 is started at a lowspeed from the state with the evacuation path shut by the valvemechanisms 201 and 202.

[0161] Next, at the injection start time Pt1, the valve mechanism 201 isopened and the pressure in the cavity C starts to be reduced. Note thatthe other valve mechanism 202 is shut in this state.

[0162] By opening the valve mechanism 201, the pressure in the cavity Cis rapidly reduced by the vacuum pump 501.

[0163] Next, when reaching the time Pt2 where the pressure in the cavityis reduced to some degree, the valve mechanism 201 is shut and the valvemechanism 202 is opened. By this, the reduction of the pressure in thecavity C is continued by the vacuum pump 502. These opening and shuttingoperations of the valve mechanisms 201 and 202 are made by outputtingcommand from the machine controllers 52 to the valve controller 51.

[0164] Note that as a characteristic of a vacuum pump, it is known thatthe evacuation speed gradually decreases along with a reduction of thepressure. For example, when the pressure is reduced by the vacuum pump501, the evacuation speed gradually falls. Due to this, by changing thevacuum pump for reducing the pressure in the cavity C to the vacuum pump502 after the reduction of pressure by the vacuum pump 501 progresses tosome extent, it becomes possible to suppress the decrease of theevacuation speed as much as possible and shorten the time required toreduce the pressure to a desirable pressure.

[0165] By reducing the pressure in the cavity by the vacuum pump 502,the cavity reaches in a high vacuum.

[0166] In this state, as shown at the time Pt3 of the curve (2), theinjection speed of the plunger tip 97 is changed to a high speed.

[0167] On the other hand, from the viewpoint of maintaining the cavityat a high vacuum, it is preferable that the timing to shut the valvemechanism 202 be as late as possible. Accordingly, even after changingto high speed injection, by leaving the valve mechanism 202 open so longas the molten metal does not reach the valve mechanism 202, it becomespossible to reliably suppress the rise of the pressure in the cavity Cafter shutting the evacuation path communicated with the vacuum pump502.

[0168] In the present embodiment, the valve mechanism 202 is shut afterchanging to high speed injection as at the time Pt4 in the curve (2).

[0169] The time required for the high speed injection is short such asfor example 40 ms to 200 ms. In the present embodiment, because of usingthe electromagnetic actuator 22 in the valve mechanism, it becomespossible to shut the valve mechanism 202 timely in such a limited time.

[0170] Further, the valve mechanism 202 is located away from the cavityC compared with the valve mechanism 201. By shutting the valve mechanism202 located apart like this last, it becomes possible to prevent themolten metal from entering into the valve mechanism while delaying thetiming to shut the evacuation path communicated with the cavity C asmuch as possible.

[0171] Summarizing the effects of the invention, as described above,according to the present invention, it is possible to provide a diecasting machine using vacuum casting which can realize a high vacuum inthe cavity.

[0172] Further, according to the present invention, it becomes possibleto efficiently reduce the pressure in the die cavity in short time.

[0173] While the invention has been described with reference to specificembodiment chosen for purpose of illustration, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the basic concept and scope of theinvention.

What is claimed is:
 1. A die casting machine comprising: a movable dieand a fixed die, a vacuum pump for reducing pressure in a cavity formedbetween the dies, and an injection apparatus for injecting and filingmolten metal into the cavity at a reduced pressure, at least one of thedies including an evacuation path connected with the vacuum pump andcommunicated with the cavity, a valve element for opening and shuttingthe evacuation path, and an electromagnetic driving means for making thevalve element move linearly in the opening and shutting direction byelectromagnetic force.
 2. A die casting machine as set forth in claim 1,wherein said valve element and said electromagnetic means are providedat the movable die side.
 3. A die casting machine as set forth in claim1, wherein at least one of the said dies is integrally provided with avalve seat portion contacting said valve element when shutting saidevacuation path.
 4. A die casting machine as set forth in claim 3,wherein said valve seat portion is made of a softer material than thatof said valve element.
 5. A die casting machine as set forth in claim 1,wherein said valve element is arranged between parting faces of saiddies and is driven in a direction vertical to the parting faces.
 6. Adie casting machine as set forth in claim 4, wherein said evacuationpath comprises a first evacuation path formed between said parting facesof said dies and communicated with said cavity and a second evacuationpath connected with an end of said first evacuation path and formedinside of said dies, and said valve seat portion is arranged at theconnecting part between said first and second evacuation path andprovided with a valve seat contactable with said valve element alongwith said parting faces.
 7. A die casting machine as set forth in claim6, further comprising a ring-shaped sealing member arranged between saidparting faces and surrounding said cavity and said first evacuationpath.
 8. A die casting machine comprising: a movable die and a fixeddie, a vacuum pump for reducing pressure in a cavity formed between thedies, and an injection apparatus for injecting and filing molten metalinto the cavity with a reduced pressure, at least one of the diesincluding: an evacuation path connected with the vacuum pump andcommunicated with the cavity, a plurality of valve elements for openingand shutting the evacuation path, a plurality of electromagnetic drivingmeans for moving the valve elements linearly in the opening and shuttingdirection by electromagnetic force, and a control means forindependently controlling the drive operations of the electromagneticmeans.
 9. A die casting machine as set forth in claim 8, wherein saiddies have a plurality of evacuation paths independently opened and shutby said valve elements, and different vacuum pump are connected withthese evacuation paths.
 10. A die casting machine as set forth in claim8, wherein said control means controls said electromagnetic drivingmeans in a predetermined order so as to reduce the pressure in thecavity in stages by changing the vacuum pumps reducing the pressure inthe cavity.
 11. A die casting machine comprising: a movable die and afixed die, a vacuum pump for reducing pressure in a cavity formedbetween the dies, an injection apparatus for injecting and filing moltenmetal into the cavity with a reduced pressure, an ejecting pin, forejecting a product formed in the cavity, inserted into an insertion holeformed in a die and communicated with the cavity, a sealing member forsealing between the ejecting pin and the insertion hole to prevent airfrom flowing into the reduced pressure cavity, and a temperature riseprevention means for preventing a rise in the temperature of theejecting pin due to contact with the formed product.
 12. A die castingmachine as set forth in claim 11, wherein said temperature riseprevention means force cools the region of the ejecting pin tightly fitwith the sealing member.
 13. A die casting machine as set forth in claim11, wherein said temperature rise prevention means has a coolant storagepart which is fixed at the back side of said dies, holds said sealingmembers, and stores coolant inside.
 14. A die casting machine as setforth in claim 13, wherein said coolant storage part is provided with asupply port supplied with said coolant and an discharge port fordischarging said coolant passing inside and said ejecting pin andpenetrates into said coolant storage part while tightly fit with saidsealing member.
 15. A die casting machine as set forth in claim 13,wherein a space for preventing conductance of heat is formed betweensaid coolant storage part and said dies.